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@johnpryan
Last active February 24, 2023 08:47
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Declarative Navigation ex. 9 - Navigation Rail + Router + Animations
import 'package:flutter/material.dart';
void main() {
runApp(NestedRouterDemo());
}
class Book {
final String title;
final String author;
Book(this.title, this.author);
}
class NestedRouterDemo extends StatefulWidget {
@override
_NestedRouterDemoState createState() => _NestedRouterDemoState();
}
class _NestedRouterDemoState extends State<NestedRouterDemo> {
BookRouterDelegate _routerDelegate = BookRouterDelegate();
BookRouteInformationParser _routeInformationParser =
BookRouteInformationParser();
@override
Widget build(BuildContext context) {
return MaterialApp.router(
title: 'Books App',
routerDelegate: _routerDelegate,
routeInformationParser: _routeInformationParser,
);
}
}
class BooksAppState extends ChangeNotifier {
int _selectedIndex;
Book _selectedBook;
final List<Book> books = [
Book('Stranger in a Strange Land', 'Robert A. Heinlein'),
Book('Foundation', 'Isaac Asimov'),
Book('Fahrenheit 451', 'Ray Bradbury'),
];
BooksAppState() : _selectedIndex = 0;
int get selectedIndex => _selectedIndex;
set selectedIndex(int idx) {
_selectedIndex = idx;
if (_selectedIndex == 1) {
// Remove this line if you want to keep the selected book when navigating
// between "settings" and "home" which book was selected when Settings is
// tapped.
selectedBook = null;
}
notifyListeners();
}
Book get selectedBook => _selectedBook;
set selectedBook(Book book) {
_selectedBook = book;
notifyListeners();
}
int getSelectedBookById() {
if (!books.contains(_selectedBook)) return 0;
return books.indexOf(_selectedBook);
}
void setSelectedBookById(int id) {
if (id < 0 || id > books.length - 1) {
return;
}
_selectedBook = books[id];
notifyListeners();
}
}
class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
@override
Future<BookRoutePath> parseRouteInformation(
RouteInformation routeInformation) async {
final uri = Uri.parse(routeInformation.location);
if (uri.pathSegments.isNotEmpty && uri.pathSegments.first == 'settings') {
return BooksSettingsPath();
} else {
if (uri.pathSegments.length >= 2) {
if (uri.pathSegments[0] == 'book') {
return BooksDetailsPath(int.tryParse(uri.pathSegments[1]));
}
}
return BooksListPath();
}
}
@override
RouteInformation restoreRouteInformation(BookRoutePath configuration) {
if (configuration is BooksListPath) {
return RouteInformation(location: '/home');
}
if (configuration is BooksSettingsPath) {
return RouteInformation(location: '/settings');
}
if (configuration is BooksDetailsPath) {
return RouteInformation(location: '/book/${configuration.id}');
}
return null;
}
}
class BookRouterDelegate extends RouterDelegate<BookRoutePath>
with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
final GlobalKey<NavigatorState> navigatorKey;
BooksAppState appState = BooksAppState();
BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>() {
appState.addListener(notifyListeners);
}
BookRoutePath get currentConfiguration {
if (appState.selectedIndex == 1) {
return BooksSettingsPath();
} else {
if (appState.selectedBook == null) {
return BooksListPath();
} else {
return BooksDetailsPath(appState.getSelectedBookById());
}
}
}
@override
Widget build(BuildContext context) {
return Navigator(
key: navigatorKey,
pages: [
MaterialPage(
child: AppShell(appState: appState),
),
],
onPopPage: (route, result) {
if (!route.didPop(result)) {
return false;
}
if (appState.selectedBook != null) {
appState.selectedBook = null;
}
notifyListeners();
return true;
},
);
}
@override
Future<void> setNewRoutePath(BookRoutePath path) async {
if (path is BooksListPath) {
appState.selectedIndex = 0;
appState.selectedBook = null;
} else if (path is BooksSettingsPath) {
appState.selectedIndex = 1;
} else if (path is BooksDetailsPath) {
appState.setSelectedBookById(path.id);
}
}
}
// Routes
abstract class BookRoutePath {}
class BooksListPath extends BookRoutePath {}
class BooksSettingsPath extends BookRoutePath {}
class BooksDetailsPath extends BookRoutePath {
final int id;
BooksDetailsPath(this.id);
}
// Widget that contains the AdaptiveNavigationScaffold
class AppShell extends StatefulWidget {
final BooksAppState appState;
AppShell({
@required this.appState,
});
@override
_AppShellState createState() => _AppShellState();
}
class _AppShellState extends State<AppShell> {
InnerRouterDelegate _routerDelegate;
ChildBackButtonDispatcher _backButtonDispatcher;
void initState() {
super.initState();
_routerDelegate = InnerRouterDelegate(widget.appState);
}
@override
void didUpdateWidget(covariant AppShell oldWidget) {
super.didUpdateWidget(oldWidget);
_routerDelegate.appState = widget.appState;
}
@override
void didChangeDependencies() {
super.didChangeDependencies();
// Defer back button dispatching to the child router
_backButtonDispatcher = Router.of(context)
.backButtonDispatcher
.createChildBackButtonDispatcher();
}
@override
Widget build(BuildContext context) {
var appState = widget.appState;
// Claim priority, If there are parallel sub router, you will need
// to pick which one should take priority;
_backButtonDispatcher.takePriority();
return Scaffold(
appBar: AppBar(),
body: Router(
routerDelegate: _routerDelegate,
backButtonDispatcher: _backButtonDispatcher,
),
bottomNavigationBar: BottomNavigationBar(
items: [
BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
BottomNavigationBarItem(
icon: Icon(Icons.settings), label: 'Settings'),
],
currentIndex: appState.selectedIndex,
onTap: (newIndex) {
appState.selectedIndex = newIndex;
},
),
);
}
}
class InnerRouterDelegate extends RouterDelegate<BookRoutePath>
with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
BooksAppState get appState => _appState;
BooksAppState _appState;
set appState(BooksAppState value) {
if (value == _appState) {
return;
}
_appState = value;
notifyListeners();
}
InnerRouterDelegate(this._appState);
@override
Widget build(BuildContext context) {
return Navigator(
key: navigatorKey,
pages: [
if (appState.selectedIndex == 0) ...[
FadeAnimationPage(
child: BooksListScreen(
books: appState.books,
onTapped: _handleBookTapped,
),
key: ValueKey('BooksListPage'),
),
if (appState.selectedBook != null)
MaterialPage(
key: ValueKey(appState.selectedBook),
child: BookDetailsScreen(book: appState.selectedBook),
),
] else
FadeAnimationPage(
child: SettingsScreen(),
key: ValueKey('SettingsPage'),
),
],
onPopPage: (route, result) {
appState.selectedBook = null;
notifyListeners();
return route.didPop(result);
},
);
}
@override
Future<void> setNewRoutePath(BookRoutePath path) async {
// This is not required for inner router delegate because it does not
// parse route
assert(false);
}
void _handleBookTapped(Book book) {
appState.selectedBook = book;
notifyListeners();
}
}
class FadeAnimationPage extends Page {
final Widget child;
FadeAnimationPage({Key key, this.child}) : super(key: key);
Route createRoute(BuildContext context) {
return PageRouteBuilder(
settings: this,
pageBuilder: (context, animation, animation2) {
var curveTween = CurveTween(curve: Curves.easeIn);
return FadeTransition(
opacity: animation.drive(curveTween),
child: child,
);
},
);
}
}
// Screens
class BooksListScreen extends StatelessWidget {
final List<Book> books;
final ValueChanged<Book> onTapped;
BooksListScreen({
@required this.books,
@required this.onTapped,
});
@override
Widget build(BuildContext context) {
return Scaffold(
body: ListView(
children: [
for (var book in books)
ListTile(
title: Text(book.title),
subtitle: Text(book.author),
onTap: () => onTapped(book),
)
],
),
);
}
}
class BookDetailsScreen extends StatelessWidget {
final Book book;
BookDetailsScreen({
@required this.book,
});
@override
Widget build(BuildContext context) {
return Scaffold(
body: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
FlatButton(
onPressed: () {
Navigator.of(context).pop();
},
child: Text('Back'),
),
if (book != null) ...[
Text(book.title, style: Theme.of(context).textTheme.headline6),
Text(book.author, style: Theme.of(context).textTheme.subtitle1),
],
],
),
),
);
}
}
class SettingsScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Text('Settings screen'),
),
);
}
}
@jonasjuni
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Thanks @xmkevinchen !!!!

@PlugFox
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PlugFox commented Mar 16, 2021

@ali-star
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ali-star commented Apr 13, 2021

The state of the home list not get saved when scrolling down the list and switching to the settings page and navigate to home again, the list scroll offset gets reset.
Does anyone know how to fix this?

import 'package:flutter/material.dart';

void main() {
  runApp(NestedRouterDemo());
}

class Book {
  final String title;
  final String author;

  Book(this.title, this.author);
}

class NestedRouterDemo extends StatefulWidget {
  @override
  _NestedRouterDemoState createState() => _NestedRouterDemoState();
}

class _NestedRouterDemoState extends State<NestedRouterDemo> {
  BookRouterDelegate _routerDelegate = BookRouterDelegate();
  BookRouteInformationParser _routeInformationParser =
      BookRouteInformationParser();

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      title: 'Books App',
      routerDelegate: _routerDelegate,
      routeInformationParser: _routeInformationParser,
    );
  }
}

class BooksAppState extends ChangeNotifier {
  int _selectedIndex;

  Book _selectedBook;

  final List<Book> books = [
    Book('Book 1', 'Ray Bradbury'),
    Book('Book 2', 'Ray Bradbury'),
    Book('Book 3', 'Ray Bradbury'),
    Book('Book 4', 'Ray Bradbury'),
    Book('Book 5', 'Ray Bradbury'),
    Book('Book 6', 'Ray Bradbury'),
    Book('Book 7', 'Ray Bradbury'),
    Book('Book 8', 'Ray Bradbury'),
    Book('Book 9', 'Ray Bradbury'),
    Book('Book 10', 'Ray Bradbury'),
    Book('Book 11', 'Ray Bradbury'),
    Book('Book 12', 'Ray Bradbury'),
    Book('Book 13', 'Ray Bradbury'),
    Book('Book 14', 'Ray Bradbury'),
    Book('Book 15', 'Ray Bradbury'),
    Book('Book 16', 'Ray Bradbury'),
    Book('Book 17', 'Ray Bradbury'),
    Book('Book 18', 'Ray Bradbury'),
    Book('Book 19', 'Ray Bradbury'),
    Book('Book 20', 'Ray Bradbury'),
    Book('Book 21', 'Ray Bradbury'),
    Book('Book 22', 'Ray Bradbury'),
    Book('Book 23', 'Ray Bradbury'),
    Book('Book 24', 'Ray Bradbury'),
    Book('Book 25', 'Ray Bradbury'),
    Book('Book 26', 'Ray Bradbury'),
    Book('Book 27', 'Ray Bradbury'),
    Book('Book 28', 'Ray Bradbury'),
    Book('Book 29', 'Ray Bradbury'),
    Book('Book 30', 'Ray Bradbury'),
    Book('Book 31', 'Ray Bradbury'),
    Book('Book 32', 'Ray Bradbury'),
    Book('Book 33', 'Ray Bradbury'),
    Book('Book 34', 'Ray Bradbury'),
    Book('Book 35', 'Ray Bradbury'),
    Book('Book 36', 'Ray Bradbury'),
    Book('Book 37', 'Ray Bradbury'),
    Book('Book 38', 'Ray Bradbury'),
    Book('Book 39', 'Ray Bradbury'),
    Book('Book 40', 'Ray Bradbury'),
    Book('Book 41', 'Ray Bradbury'),
    Book('Book 42', 'Ray Bradbury'),
    Book('Book 43', 'Ray Bradbury'),
  ];

  BooksAppState() : _selectedIndex = 0;

  int get selectedIndex => _selectedIndex;

  set selectedIndex(int idx) {
    _selectedIndex = idx;
    if (_selectedIndex == 1) {
      // Remove this line if you want to keep the selected book when navigating
      // between "settings" and "home" which book was selected when Settings is
      // tapped.
      // selectedBook = null;
    }
    notifyListeners();
  }

  Book get selectedBook => _selectedBook;

  set selectedBook(Book book) {
    _selectedBook = book;
    notifyListeners();
  }

  int getSelectedBookById() {
    if (!books.contains(_selectedBook)) return 0;
    return books.indexOf(_selectedBook);
  }

  void setSelectedBookById(int id) {
    if (id < 0 || id > books.length - 1) {
      return;
    }

    _selectedBook = books[id];
    notifyListeners();
  }
}

class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
  @override
  Future<BookRoutePath> parseRouteInformation(
      RouteInformation routeInformation) async {
    final uri = Uri.parse(routeInformation.location);

    if (uri.pathSegments.isNotEmpty && uri.pathSegments.first == 'settings') {
      return BooksSettingsPath();
    } else {
      if (uri.pathSegments.length >= 2) {
        if (uri.pathSegments[0] == 'book') {
          return BooksDetailsPath(int.tryParse(uri.pathSegments[1]));
        }
      }
      return BooksListPath();
    }
  }

  @override
  RouteInformation restoreRouteInformation(BookRoutePath configuration) {
    if (configuration is BooksListPath) {
      return RouteInformation(location: '/home');
    }
    if (configuration is BooksSettingsPath) {
      return RouteInformation(location: '/settings');
    }
    if (configuration is BooksDetailsPath) {
      return RouteInformation(location: '/book/${configuration.id}');
    }
    return null;
  }
}

class BookRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  final GlobalKey<NavigatorState> navigatorKey;

  BooksAppState appState = BooksAppState();

  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>() {
    appState.addListener(notifyListeners);
  }

  BookRoutePath get currentConfiguration {
    if (appState.selectedIndex == 1) {
      return BooksSettingsPath();
    } else {
      if (appState.selectedBook == null) {
        return BooksListPath();
      } else {
        return BooksDetailsPath(appState.getSelectedBookById());
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        MaterialPage(
          child: AppShell(appState: appState),
        ),
      ],
      onPopPage: (route, result) {
        if (!route.didPop(result)) {
          return false;
        }

        if (appState.selectedBook != null) {
          appState.selectedBook = null;
        }
        notifyListeners();
        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath path) async {
    if (path is BooksListPath) {
      appState.selectedIndex = 0;
      appState.selectedBook = null;
    } else if (path is BooksSettingsPath) {
      appState.selectedIndex = 1;
    } else if (path is BooksDetailsPath) {
      appState.setSelectedBookById(path.id);
    }
  }
}

// Routes
abstract class BookRoutePath {}

class BooksListPath extends BookRoutePath {}

class BooksSettingsPath extends BookRoutePath {}

class BooksDetailsPath extends BookRoutePath {
  final int id;

  BooksDetailsPath(this.id);
}

// Widget that contains the AdaptiveNavigationScaffold
class AppShell extends StatefulWidget {
  final BooksAppState appState;

  AppShell({
    @required this.appState,
  });

  @override
  _AppShellState createState() => _AppShellState();
}

class _AppShellState extends State<AppShell> {
  InnerRouterDelegate _routerDelegate;
  ChildBackButtonDispatcher _backButtonDispatcher;

  void initState() {
    super.initState();
    _routerDelegate = InnerRouterDelegate(widget.appState);
  }

  @override
  void didUpdateWidget(covariant AppShell oldWidget) {
    super.didUpdateWidget(oldWidget);
    _routerDelegate.appState = widget.appState;
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Defer back button dispatching to the child router
    _backButtonDispatcher = Router.of(context)
        .backButtonDispatcher
        .createChildBackButtonDispatcher();
  }

  @override
  Widget build(BuildContext context) {
    var appState = widget.appState;

    // Claim priority, If there are parallel sub router, you will need
    // to pick which one should take priority;
    _backButtonDispatcher.takePriority();

    return Scaffold(
      appBar: AppBar(),
      body: Router(
        routerDelegate: _routerDelegate,
        backButtonDispatcher: _backButtonDispatcher,
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings), label: 'Settings'),
        ],
        currentIndex: appState.selectedIndex,
        onTap: (newIndex) {
          appState.selectedIndex = newIndex;
        },
      ),
    );
  }
}

class InnerRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();

  BooksAppState get appState => _appState;
  BooksAppState _appState;

  set appState(BooksAppState value) {
    if (value == _appState) {
      return;
    }
    _appState = value;
    notifyListeners();
  }

  InnerRouterDelegate(this._appState);

  FadeAnimationPage listPage;

  FadeAnimationPage getList() {
    if (listPage == null)
      listPage = FadeAnimationPage(
        child: BooksListScreen(
          books: appState.books,
          onTapped: _handleBookTapped,
        ),
        key: ValueKey('BooksListPage'),
      );

    return listPage;
  }

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        if (appState.selectedIndex == 0) ...[
          getList(),
          if (appState.selectedBook != null)
            MaterialPage(
              key: ValueKey(appState.selectedBook),
              child: BookDetailsScreen(book: appState.selectedBook),
            ),
        ] else
          FadeAnimationPage(
            child: SettingsScreen(),
            key: ValueKey('SettingsPage'),
          ),
      ],
      onPopPage: (route, result) {
        appState.selectedBook = null;
        notifyListeners();
        return route.didPop(result);
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath path) async {
    // This is not required for inner router delegate because it does not
    // parse route
    assert(false);
  }

  void _handleBookTapped(Book book) {
    appState.selectedBook = book;
    notifyListeners();
  }
}

class FadeAnimationPage extends Page {
  final Widget child;

  FadeAnimationPage({Key key, this.child}) : super(key: key);

  Route createRoute(BuildContext context) {
    return PageRouteBuilder(
      settings: this,
      pageBuilder: (context, animation, animation2) {
        var curveTween = CurveTween(curve: Curves.easeIn);
        return FadeTransition(
          opacity: animation.drive(curveTween),
          child: child,
        );
      },
    );
  }
}

// Screens
class BooksListScreen extends StatelessWidget {
  final List<Book> books;
  final ValueChanged<Book> onTapped;

  BooksListScreen({
    @required this.books,
    @required this.onTapped,
  }));

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: [
          for (var book in books)
            ListTile(
              title: Text(book.title),
              subtitle: Text(book.author),
              onTap: () => onTapped(book),
            )
        ],
      ),
    );
  }
}

class BookDetailsScreen extends StatelessWidget {
  final Book book;

  BookDetailsScreen({
    @required this.book,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            FlatButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: Text('Back'),
            ),
            if (book != null) ...[
              Text(book.title, style: Theme.of(context).textTheme.headline6),
              Text(book.author, style: Theme.of(context).textTheme.subtitle1),
            ],
          ],
        ),
      ),
    );
  }
}

class SettingsScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text('Settings screen'),
      ),
    );
  }
}

@dleurs
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dleurs commented Aug 16, 2021

Upgrade to flutter sdk >= 2.12

import 'package:flutter/material.dart';

void main() {
  runApp(NestedRouterDemo());
}

class Book {
  final String title;
  final String author;

  Book(this.title, this.author);
}

class NestedRouterDemo extends StatefulWidget {
  @override
  _NestedRouterDemoState createState() => _NestedRouterDemoState();
}

class _NestedRouterDemoState extends State<NestedRouterDemo> {
  BookRouterDelegate _routerDelegate = BookRouterDelegate();
  BookRouteInformationParser _routeInformationParser = BookRouteInformationParser();

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      title: 'Books App',
      routerDelegate: _routerDelegate,
      routeInformationParser: _routeInformationParser,
    );
  }
}

class BooksAppState extends ChangeNotifier {
  int _selectedIndex;

  Book? _selectedBook;

  final List<Book> books = [
    Book('Stranger in a Strange Land', 'Robert A. Heinlein'),
    Book('Foundation', 'Isaac Asimov'),
    Book('Fahrenheit 451', 'Ray Bradbury'),
  ];

  BooksAppState() : _selectedIndex = 0;

  int get selectedIndex => _selectedIndex;

  set selectedIndex(int idx) {
    _selectedIndex = idx;
    notifyListeners();
  }

  Book? get selectedBook => _selectedBook;

  set selectedBook(Book? book) {
    _selectedBook = book;
    notifyListeners();
  }

  int? getSelectedBookById() {
    if (_selectedBook == null || !books.contains(_selectedBook)) return null;
    return books.indexOf(_selectedBook!);
  }

  void setSelectedBookById(int id) {
    if (id < 0 || id > books.length - 1) {
      return;
    }

    _selectedBook = books[id];
    notifyListeners();
  }
}

class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
  @override
  Future<BookRoutePath> parseRouteInformation(RouteInformation routeInformation) async {
    final uri = Uri.parse(routeInformation.location ?? '');

    if (uri.pathSegments.isNotEmpty && uri.pathSegments.first == 'settings') {
      return BooksSettingsPath();
    } else {
      if (uri.pathSegments.length >= 2) {
        if (uri.pathSegments[0] == 'book') {
          return BooksDetailsPath(int.tryParse(uri.pathSegments[1]));
        }
      }
      return BooksListPath();
    }
  }

  @override
  RouteInformation restoreRouteInformation(BookRoutePath configuration) {
    if (configuration is BooksListPath) {
      return RouteInformation(location: '/home');
    }
    if (configuration is BooksSettingsPath) {
      return RouteInformation(location: '/settings');
    }
    if (configuration is BooksDetailsPath) {
      return RouteInformation(location: '/book/${configuration.id}');
    }
    return RouteInformation();
  }
}

class BookRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  final GlobalKey<NavigatorState> navigatorKey;

  BooksAppState appState = BooksAppState();

  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>() {
    appState.addListener(notifyListeners);
  }

  BookRoutePath get currentConfiguration {
    if (appState.selectedIndex == 1) {
      return BooksSettingsPath();
    } else {
      if (appState.selectedBook == null) {
        return BooksListPath();
      } else {
        return BooksDetailsPath(appState.getSelectedBookById());
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        MaterialPage(
          child: AppShell(appState: appState),
        ),
      ],
      onPopPage: (route, result) {
        if (!route.didPop(result)) {
          return false;
        }

        if (appState.selectedBook != null) {
          appState.selectedBook = null;
        }
        notifyListeners();
        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath path) async {
    if (path is BooksListPath) {
      appState.selectedIndex = 0;
      appState.selectedBook = null;
    } else if (path is BooksSettingsPath) {
      appState.selectedIndex = 1;
    } else if (path is BooksDetailsPath && path.id != null) {
      appState.setSelectedBookById(path.id!);
    }
  }
}

// Routes
abstract class BookRoutePath {}

class BooksListPath extends BookRoutePath {}

class BooksSettingsPath extends BookRoutePath {}

class BooksDetailsPath extends BookRoutePath {
  final int? id;

  BooksDetailsPath(this.id);
}

// Widget that contains the AdaptiveNavigationScaffold
class AppShell extends StatefulWidget {
  final BooksAppState appState;

  AppShell({
    required this.appState,
  });

  @override
  _AppShellState createState() => _AppShellState();
}

class _AppShellState extends State<AppShell> {
  late InnerRouterDelegate _routerDelegate;
  late ChildBackButtonDispatcher _backButtonDispatcher;

  void initState() {
    super.initState();
    _routerDelegate = InnerRouterDelegate(widget.appState);
  }

  @override
  void didUpdateWidget(covariant AppShell oldWidget) {
    super.didUpdateWidget(oldWidget);
    _routerDelegate.appState = widget.appState;
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Defer back button dispatching to the child router
    _backButtonDispatcher = Router.of(context).backButtonDispatcher!.createChildBackButtonDispatcher();
  }

  @override
  Widget build(BuildContext context) {
    var appState = widget.appState;

    // Claim priority, If there are parallel sub router, you will need
    // to pick which one should take priority;
    _backButtonDispatcher.takePriority();

    return Scaffold(
      appBar: AppBar(),
      body: Router(
        routerDelegate: _routerDelegate,
        backButtonDispatcher: _backButtonDispatcher,
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(icon: Icon(Icons.settings), label: 'Settings'),
        ],
        currentIndex: appState.selectedIndex,
        onTap: (newIndex) {
          appState.selectedIndex = newIndex;
        },
      ),
    );
  }
}

class InnerRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
  BooksAppState get appState => _appState;
  BooksAppState _appState;
  set appState(BooksAppState value) {
    if (value == _appState) {
      return;
    }
    _appState = value;
    notifyListeners();
  }

  InnerRouterDelegate(this._appState);

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        if (appState.selectedIndex == 0) ...[
          FadeAnimationPage(
            child: BooksListScreen(
              books: appState.books,
              onTapped: _handleBookTapped,
            ),
            key: ValueKey('BooksListPage'),
          ),
          if (appState.selectedBook != null)
            MaterialPage(
              key: ValueKey(appState.selectedBook),
              child: BookDetailsScreen(book: appState.selectedBook!),
            ),
        ] else
          FadeAnimationPage(
            child: SettingsScreen(),
            key: ValueKey('SettingsPage'),
          ),
      ],
      onPopPage: (route, result) {
        appState.selectedBook = null;
        notifyListeners();
        return route.didPop(result);
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath path) async {
    // This is not required for inner router delegate because it does not
    // parse route
    assert(false);
  }

  void _handleBookTapped(Book book) {
    appState.selectedBook = book;
    notifyListeners();
  }
}

class FadeAnimationPage extends Page {
  final Widget child;

  FadeAnimationPage({required LocalKey key, required this.child}) : super(key: key);

  Route createRoute(BuildContext context) {
    return PageRouteBuilder(
      settings: this,
      pageBuilder: (context, animation, animation2) {
        var curveTween = CurveTween(curve: Curves.easeIn);
        return FadeTransition(
          opacity: animation.drive(curveTween),
          child: child,
        );
      },
    );
  }
}

// Screens
class BooksListScreen extends StatelessWidget {
  final List<Book> books;
  final ValueChanged<Book> onTapped;

  BooksListScreen({
    required this.books,
    required this.onTapped,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: [
          for (var book in books)
            ListTile(
              title: Text(book.title),
              subtitle: Text(book.author),
              onTap: () => onTapped(book),
            )
        ],
      ),
    );
  }
}

class BookDetailsScreen extends StatelessWidget {
  final Book book;

  BookDetailsScreen({
    required this.book,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            ElevatedButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: Text('Back'),
            ),
            Text(book.title, style: Theme.of(context).textTheme.headline6),
            Text(book.author, style: Theme.of(context).textTheme.subtitle1),
          ],
        ),
      ),
    );
  }
}

class SettingsScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text('Settings screen'),
      ),
    );
  }
}

@atsuya
Copy link

atsuya commented May 16, 2022

If you are retrieving a list of books from Firestore (or some API), how do you refresh a list of books listed on BooksListScreen when coming back from BookDetailsScreen? Let's say you add a new book on BookDetailsScreen, then you probably want to show the new book added to the list of books when coming back to BooksListScreen.

@TinoCarrera
Copy link

Upgrade to Flutter SDK >= 3.0.0

import 'package:flutter/material.dart';

void main() {
  runApp(const NestedRouterDemo());
}

class Book {
  final String title;
  final String author;

  Book(this.title, this.author);
}

class NestedRouterDemo extends StatefulWidget {
  const NestedRouterDemo({Key? key}) : super(key: key);

  @override
  State<NestedRouterDemo> createState() => _NestedRouterDemoState();
}

class _NestedRouterDemoState extends State<NestedRouterDemo> {
  final BookRouterDelegate _routerDelegate = BookRouterDelegate();
  final BookRouteInformationParser _routeInformationParser =
      BookRouteInformationParser();

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      title: 'Books App',
      routerDelegate: _routerDelegate,
      routeInformationParser: _routeInformationParser,
    );
  }
}

class BooksAppState extends ChangeNotifier {
  int _selectedIndex;

  Book? _selectedBook;

  final List<Book> books = [
    Book('Stranger in a Strange Land', 'Robert A. Heinlein'),
    Book('Foundation', 'Isaac Asimov'),
    Book('Fahrenheit 451', 'Ray Bradbury'),
  ];

  BooksAppState() : _selectedIndex = 0;

  int get selectedIndex => _selectedIndex;

  set selectedIndex(int idx) {
    _selectedIndex = idx;
    notifyListeners();
  }

  Book? get selectedBook => _selectedBook;

  set selectedBook(Book? book) {
    _selectedBook = book;
    notifyListeners();
  }

  int? getSelectedBookById() {
    if (_selectedBook == null || !books.contains(_selectedBook)) return null;
    return books.indexOf(_selectedBook!);
  }

  void setSelectedBookById(int id) {
    if (id < 0 || id > books.length - 1) {
      return;
    }

    _selectedBook = books[id];
    notifyListeners();
  }
}

class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
  @override
  Future<BookRoutePath> parseRouteInformation(
      RouteInformation routeInformation) async {
    final uri = Uri.parse(routeInformation.location ?? '');

    if (uri.pathSegments.isNotEmpty && uri.pathSegments.first == 'settings') {
      return BooksSettingsPath();
    } else {
      if (uri.pathSegments.length >= 2) {
        if (uri.pathSegments[0] == 'book') {
          return BooksDetailsPath(int.tryParse(uri.pathSegments[1]));
        }
      }
      return BooksListPath();
    }
  }

  @override
  RouteInformation restoreRouteInformation(BookRoutePath configuration) {
    if (configuration is BooksListPath) {
      return const RouteInformation(location: '/home');
    }
    if (configuration is BooksSettingsPath) {
      return const RouteInformation(location: '/settings');
    }
    if (configuration is BooksDetailsPath) {
      return RouteInformation(location: '/book/${configuration.id}');
    }
    return const RouteInformation();
  }
}

class BookRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  @override
  final GlobalKey<NavigatorState> navigatorKey;

  BooksAppState appState = BooksAppState();

  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>() {
    appState.addListener(notifyListeners);
  }

  @override
  BookRoutePath get currentConfiguration {
    if (appState.selectedIndex == 1) {
      return BooksSettingsPath();
    } else {
      if (appState.selectedBook == null) {
        return BooksListPath();
      } else {
        return BooksDetailsPath(appState.getSelectedBookById());
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        MaterialPage(
          child: AppShell(appState: appState),
        ),
      ],
      onPopPage: (route, result) {
        if (!route.didPop(result)) {
          return false;
        }

        if (appState.selectedBook != null) {
          appState.selectedBook = null;
        }
        notifyListeners();
        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath configuration) async {
    if (configuration is BooksListPath) {
      appState.selectedIndex = 0;
      appState.selectedBook = null;
    } else if (configuration is BooksSettingsPath) {
      appState.selectedIndex = 1;
    } else if (configuration is BooksDetailsPath && configuration.id != null) {
      appState.setSelectedBookById(configuration.id!);
    }
  }
}

// Routes
abstract class BookRoutePath {}

class BooksListPath extends BookRoutePath {}

class BooksSettingsPath extends BookRoutePath {}

class BooksDetailsPath extends BookRoutePath {
  final int? id;

  BooksDetailsPath(this.id);
}

// Widget that contains the AdaptiveNavigationScaffold
class AppShell extends StatefulWidget {
  const AppShell({
    Key? key,
    required this.appState,
  }) : super(key: key);

  final BooksAppState appState;

  @override
  State<AppShell> createState() => _AppShellState();
}

class _AppShellState extends State<AppShell> {
  late InnerRouterDelegate _routerDelegate;
  late ChildBackButtonDispatcher _backButtonDispatcher;

  @override
  void initState() {
    super.initState();
    _routerDelegate = InnerRouterDelegate(widget.appState);
  }

  @override
  void didUpdateWidget(covariant AppShell oldWidget) {
    super.didUpdateWidget(oldWidget);
    _routerDelegate.appState = widget.appState;
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Defer back button dispatching to the child router
    _backButtonDispatcher = Router.of(context)
        .backButtonDispatcher!
        .createChildBackButtonDispatcher();
  }

  @override
  Widget build(BuildContext context) {
    var appState = widget.appState;

    // Claim priority, If there are parallel sub router, you will need
    // to pick which one should take priority;
    _backButtonDispatcher.takePriority();

    return Scaffold(
      appBar: AppBar(),
      body: Router(
        routerDelegate: _routerDelegate,
        backButtonDispatcher: _backButtonDispatcher,
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings), label: 'Settings'),
        ],
        currentIndex: appState.selectedIndex,
        onTap: (newIndex) {
          appState.selectedIndex = newIndex;
        },
      ),
    );
  }
}

class InnerRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  @override
  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
  BooksAppState get appState => _appState;
  BooksAppState _appState;
  set appState(BooksAppState value) {
    if (value == _appState) {
      return;
    }
    _appState = value;
    notifyListeners();
  }

  InnerRouterDelegate(this._appState);

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: navigatorKey,
      pages: [
        if (appState.selectedIndex == 0) ...[
          FadeAnimationPage(
            child: BooksListScreen(
              books: appState.books,
              onTapped: _handleBookTapped,
            ),
            key: const ValueKey('BooksListPage'),
          ),
          if (appState.selectedBook != null)
            MaterialPage(
              key: ValueKey(appState.selectedBook),
              child: BookDetailsScreen(book: appState.selectedBook!),
            ),
        ] else
          const FadeAnimationPage(
            child: SettingsScreen(),
            key: ValueKey('SettingsPage'),
          ),
      ],
      onPopPage: (route, result) {
        appState.selectedBook = null;
        notifyListeners();
        return route.didPop(result);
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath configuration) async {
    // This is not required for inner router delegate because it does not
    // parse route
    assert(false);
  }

  void _handleBookTapped(Book book) {
    appState.selectedBook = book;
    notifyListeners();
  }
}

class FadeAnimationPage extends Page {
  const FadeAnimationPage({required LocalKey key, required this.child})
      : super(key: key);

  final Widget child;

  @override
  Route createRoute(BuildContext context) {
    return PageRouteBuilder(
      settings: this,
      pageBuilder: (context, animation, animation2) {
        var curveTween = CurveTween(curve: Curves.easeIn);
        return FadeTransition(
          opacity: animation.drive(curveTween),
          child: child,
        );
      },
    );
  }
}

// Screens
class BooksListScreen extends StatelessWidget {
  const BooksListScreen({
    Key? key,
    required this.books,
    required this.onTapped,
  }) : super(key: key);

  final List<Book> books;
  final ValueChanged<Book> onTapped;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView(
        children: [
          for (var book in books)
            ListTile(
              title: Text(book.title),
              subtitle: Text(book.author),
              onTap: () => onTapped(book),
            )
        ],
      ),
    );
  }
}

class BookDetailsScreen extends StatelessWidget {
  const BookDetailsScreen({Key? key, required this.book}) : super(key: key);

  final Book book;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            ElevatedButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: const Text('Back'),
            ),
            Text(book.title, style: Theme.of(context).textTheme.headline6),
            Text(book.author, style: Theme.of(context).textTheme.subtitle1),
          ],
        ),
      ),
    );
  }
}

class SettingsScreen extends StatelessWidget {
  const SettingsScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Center(
        child: Text('Settings screen'),
      ),
    );
  }
}

@eximius313
Copy link

eximius313 commented Jan 22, 2023

  1. Why calling notifyListeners(); in
onPopPage: (route, result) {
  if (!route.didPop(result)) {
     return false;
   }

   if (appState.selectedBook != null) {
     appState.selectedBook = null;
   }
   notifyListeners();
   return true;
},

?

If we change appState.selectedBook = null; then listeners will be called by the appState.addListener(notifyListeners); isn't they?

  1. Why do we do _routerDelegate.appState = widget.appState in:
@override
void didUpdateWidget(covariant AppShell oldWidget) {
  super.didUpdateWidget(oldWidget);
  _routerDelegate.appState = widget.appState;
}

?

isn't appState passed to InnerRouterDelegate by reference, and so all the changes in the internals are reflected there?

  1. Why we do appState.selectedBook = null; in:
 onPopPage: (route, result) {
  appState.selectedBook = null;
  notifyListeners();
  return route.didPop(result);
}

instead of calling _handleBookTapped(null) that we already have?

  1. Why AppShell is StatefulWidget since it doesn't hold any state and
    _backButtonDispatcher = Router.of(context)
        .backButtonDispatcher!
        .createChildBackButtonDispatcher();

could be done in 'build` method?

Anyway - this seem to work exactly the same:

import 'package:flutter/material.dart';

void main() {
  runApp(const NestedRouterDemo());
}

class Book {
  final String title;
  final String author;

  Book(this.title, this.author);
}

class NestedRouterDemo extends StatefulWidget {
  const NestedRouterDemo({Key? key}) : super(key: key);

  @override
  State<NestedRouterDemo> createState() => _NestedRouterDemoState();
}

class _NestedRouterDemoState extends State<NestedRouterDemo> {
  final BookRouterDelegate _routerDelegate = BookRouterDelegate();
  final BookRouteInformationParser _routeInformationParser =
      BookRouteInformationParser();

  @override
  Widget build(BuildContext context) => MaterialApp.router(
      title: 'Books App',
      routerDelegate: _routerDelegate,
      routeInformationParser: _routeInformationParser,
    );
}

class BooksAppState extends ChangeNotifier {
  int _selectedIndex;

  Book? _selectedBook;

  final List<Book> books = [
    Book('Stranger in a Strange Land', 'Robert A. Heinlein'),
    Book('Foundation', 'Isaac Asimov'),
    Book('Fahrenheit 451', 'Ray Bradbury'),
  ];

  BooksAppState() : _selectedIndex = 0;

  int get selectedIndex => _selectedIndex;

  set selectedIndex(int idx) {
    _selectedIndex = idx;
    notifyListeners();
  }

  Book? get selectedBook => _selectedBook;

  set selectedBook(Book? book) {
    _selectedBook = book;
    notifyListeners();
  }

  int? getSelectedBookById() {
    if (_selectedBook == null || !books.contains(_selectedBook)) {
      return null;
    }
    return books.indexOf(_selectedBook!);
  }

  void setSelectedBookById(int id) {
    if (id < 0 || id > books.length - 1) {
      return;
    }

    _selectedBook = books[id];
    notifyListeners();
  }
}

class BookRouteInformationParser extends RouteInformationParser<BookRoutePath> {
  @override
  Future<BookRoutePath> parseRouteInformation(
      RouteInformation routeInformation) async {
    final uri = Uri.parse(routeInformation.location ?? '');

    if (uri.pathSegments.isNotEmpty && uri.pathSegments.first == 'settings') {
      return BooksSettingsPath();
    } else {
      if (uri.pathSegments.length >= 2) {
        if (uri.pathSegments[0] == 'book') {
          return BooksDetailsPath(int.tryParse(uri.pathSegments[1]));
        }
      }
      return BooksListPath();
    }
  }

  @override
  RouteInformation restoreRouteInformation(BookRoutePath configuration) {
    if (configuration is BooksListPath) {
      return const RouteInformation(location: '/home');
    }
    if (configuration is BooksSettingsPath) {
      return const RouteInformation(location: '/settings');
    }
    if (configuration is BooksDetailsPath) {
      return RouteInformation(location: '/book/${configuration.id}');
    }
    return const RouteInformation();
  }
}

class BookRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  @override
  final GlobalKey<NavigatorState> navigatorKey;

  BooksAppState appState = BooksAppState();

  BookRouterDelegate() : navigatorKey = GlobalKey<NavigatorState>() {
    appState.addListener(notifyListeners);
  }

  @override
  BookRoutePath get currentConfiguration {
    if (appState.selectedIndex == 1) {
      return BooksSettingsPath();
    } else {
      if (appState.selectedBook == null) {
        return BooksListPath();
      } else {
        return BooksDetailsPath(appState.getSelectedBookById());
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    print('BookRouterDelegate#build');
    return Navigator(
      key: navigatorKey,
      pages: [
        MaterialPage(
          child: AppShell(appState: appState),
        ),
      ],
      onPopPage: (route, result) {
        print('BookRouterDelegate#onPopPage');
        if (!route.didPop(result)) {
          return false;
        }

        if (appState.selectedBook != null) {
          appState.selectedBook = null;
        }

        return true;
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath configuration) async {
    if (configuration is BooksListPath) {
      appState.selectedIndex = 0;
      appState.selectedBook = null;
    } else if (configuration is BooksSettingsPath) {
      appState.selectedIndex = 1;
    } else if (configuration is BooksDetailsPath && configuration.id != null) {
      appState.setSelectedBookById(configuration.id!);
    }
  }
}

// Routes
abstract class BookRoutePath {}

class BooksListPath extends BookRoutePath {}

class BooksSettingsPath extends BookRoutePath {}

class BooksDetailsPath extends BookRoutePath {
  final int? id;

  BooksDetailsPath(this.id);
}

// Widget that contains the AdaptiveNavigationScaffold
class AppShell extends StatelessWidget {
  AppShell({
    Key? key,
    required this.appState,
  }) :  _routerDelegate = InnerRouterDelegate(appState), super(key: key);

  final BooksAppState appState;
  final InnerRouterDelegate _routerDelegate;

  @override
  Widget build(BuildContext context) {
    // Defer back button dispatching to the child router
    final ChildBackButtonDispatcher _backButtonDispatcher = Router.of(context)
        .backButtonDispatcher!
        .createChildBackButtonDispatcher();

    // Claim priority, If there are parallel sub router, you will need
    // to pick which one should take priority;
    _backButtonDispatcher.takePriority();

    return Scaffold(
      appBar: AppBar(),
      body: SafeArea(
        top: false,
        child: Router(
        routerDelegate: _routerDelegate,
        backButtonDispatcher: _backButtonDispatcher,
        ),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
          BottomNavigationBarItem(
              icon: Icon(Icons.settings), label: 'Settings'),
        ],
        currentIndex: appState.selectedIndex,
        onTap: (newIndex) {
          appState.selectedIndex = newIndex;
        },
      ),
    );
  }
}

class InnerRouterDelegate extends RouterDelegate<BookRoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<BookRoutePath> {
  
  @override
  final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();

  BooksAppState appState;

  InnerRouterDelegate(this.appState) {
    //not really needed, since InnerRouterDelegate is rebuild anyway everytime when BookRouterDelegate is rebuild
    //appState.addListener(notifyListeners);
  }

  @override
  Widget build(BuildContext context) {
    print('InnerRouterDelegate#build');
    return Navigator(
      key: navigatorKey,
      pages: [
        if (appState.selectedIndex == 0) ...[
          FadeAnimationPage(
            child: BooksListScreen(
              books: appState.books,
              onTapped: _handleBookTapped,
            ),
            key: const ValueKey('BooksListPage'),
          ),
          if (appState.selectedBook != null)
            MaterialPage(
              key: ValueKey(appState.selectedBook),
              child: BookDetailsScreen(book: appState.selectedBook!),
            ),
        ] else
          const FadeAnimationPage(
            child: SettingsScreen(),
            key: ValueKey('SettingsPage'),
          ),
      ],
      onPopPage: (route, result) {
        print('InnerRouterDelegate#onPopPage');
        _handleBookTapped(null);
        return route.didPop(result);
      },
    );
  }

  @override
  Future<void> setNewRoutePath(BookRoutePath configuration) async {
    // This is not required for inner router delegate because it does not parse route
    assert(false);
  }

  void _handleBookTapped(Book? book) {
    appState.selectedBook = book;
  }
}

class FadeAnimationPage extends Page {
  const FadeAnimationPage({required LocalKey key, required this.child})
      : super(key: key);

  final Widget child;

  @override
  Route createRoute(BuildContext context) {
    return PageRouteBuilder(
      settings: this,
      pageBuilder: (context, animation, animation2) {
        var curveTween = CurveTween(curve: Curves.easeIn);
        return FadeTransition(
          opacity: animation.drive(curveTween),
          child: child,
        );
      },
    );
  }
}

// Screens
class BooksListScreen extends StatelessWidget {
  const BooksListScreen({
    Key? key,
    required this.books,
    required this.onTapped,
  }) : super(key: key);

  final List<Book> books;
  final ValueChanged<Book> onTapped;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // appBar: AppBar(),
      body: ListView(
        children: [
          for (var book in books)
            ListTile(
              title: Text(book.title),
              subtitle: Text(book.author),
              onTap: () {
                onTapped(book);
              },
            )
        ],
      ),
    );
  }
}

class BookDetailsScreen extends StatelessWidget {
  const BookDetailsScreen({Key? key, required this.book}) : super(key: key);

  final Book book;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // appBar: AppBar(), //if we want the AppBar back button to appear
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            ElevatedButton(
              onPressed: () {
                Navigator.of(context).pop();
              },
              child: const Text('Back'),
            ),
            Text(book.title, style: Theme.of(context).textTheme.titleLarge),
            Text(book.author, style: Theme.of(context).textTheme.titleMedium),
          ],
        ),
      ),
    );
  }
}

class SettingsScreen extends StatelessWidget {
  const SettingsScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) => const Scaffold(
      // appBar: AppBar(),
      body: Center(
        child: Text('Settings screen'),
      ),
    );
}

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